Without the Calibration Grid Set, calibration can be performed with a paper printout which is subject to improper dimensional scaling by your 2d printer and is difficult to get to lay flat to view the entire build area simultaneously.
This Set comes with a grid for 30, 50, and 70 micron settings. All grids come with etched circles and lines that precisely match the calibration image projected by your B9Creator.
The etched lines and circles allow for easy alignment with the projected calibration image and light up when the image is calibrated (sized properly).
The etched rectangles on each side and circle in the center make it easy to determine when the projector is focused properly.